The present invention is related to miniaturized fiberoptic devices and, in particular, to highly miniaturized wavelength fiberoptic filters.
In WDM (Wavelength Division Multiplexing) and DWDM (Dense Wavelength Division Multiplexing) fiberoptic networks, optical signals are directed through the network on optical fibers according to the wavelength of the optical signals. Optical signals of a particular wavelength define a communication channel of a network which directs signals to their destinations according to their wavelengths. One element of such fiberoptic networks is the wavelength filter which passes or blocks optical signals according to their wavelengths. Heretofore, fiberoptic filter devices have been compact, but limited by the size of the discrete elements, such as a GRIN (GRaded INdex) lens which is commonly used to form the filter. Manufacture of such wavelength filter devices requires assembly of such separate elements.
On the other hand, the present invention allows for a fiberoptic filter device which is highly miniaturized and which is limited in size only by the dimensions of the optical fiber.
The present invention provides for a miniature fiberoptic filter which has a first optical fiber with a first multimode optical fiber segment attached to an end of the first optical fiber, a second multimode optical fiber segment attached to the first multimode optical fiber segment, and a plurality of dielectric coatings on an end of the second multimode optical fiber segment opposite the first multimode optical fiber segment. The first multimode optical fiber segment has a step index with its core axially aligned with the core of the first optical fiber, and the second multimode optical fiber segment has a graded index of refraction core axially aligned with the core of the first multimode optical fiber segment. The lengths of the first and second multimode optical fiber segments are selected to define a collimation and focusing function for light from and to the first optical fiber. The plurality of dielectric coatings form a wavelength-dependent optical filter.
The miniature fiberoptic filter also has a second optical fiber with a third multimode optical fiber segment attached to an end of the second optical fiber, and a fourth multimode optical fiber segment attached to the third multimode optical fiber segment. The third multimode optical fiber segment has a step index with its core axially aligned with a core of the second optical fiber, and the fourth multimode optical fiber segment has a graded index of refraction core axially aligned with the core of the third multimode optical fiber segment. The lengths of the third and fourth multimode optical fiber segments are selected to define a collimation and focusing function for light from and to the second optical fiber which is aligned with the first optical fiber so that the end of the fourth multimode optical fiber opposite the third multimode optical fiber segment faces the end of the second multimode optical fiber segment. The first optical fiber, the first multimode optical fiber segment, the second multimode optical fiber segment, the plurality of dielectric coatings, the second optical fiber, the third multimode optical fiber segment, and the fourth multimode optical fiber segment arranged and oriented with each other so light from the core of the first optical fiber passing through the plurality of dielectric coatings enters the core of the second optical fiber.
The present invention also provides for a method of manufacturing a miniature fiberoptic filter which has the steps of fixing first and second multimode fiber segments to a first optical fiber end section, the first multimode fiber segment placed between the first optical fiber end section and the second multimode fiber segment, with the first multimode fiber segment having a step index of refraction and the second multimode fiber segment having a graded index of refraction core; selecting lengths of the first and second multimode fiber segments to define a collimation and focusing function for light from and to the first optical fiber end section; depositing a plurality of dielectric layers upon an end surface of the second multimode fiber segment opposite the first multimode fiber segment, the plurality of dielectric layers defining a wavelength-dependent filtering function; fixing third and fourth multimode fiber segments to a second optical fiber end section, the third multimode fiber segment between the second optical fiber end section and the fourth multimode fiber segment, the third multimode fiber segment having a step index of refraction and the fourth multimode fiber segment having a graded index of refraction core; selecting lengths of the third and fourth multimode fiber segments to define a collimation and focusing function for light from and to the second optical fiber end section; and arranging and orienting the first optical fiber end section and fixed first and second multimode fiber segments with the second optical fiber end section and fixed third and fourth multimode fiber segments so light from a core of the first optical fiber end section passing through the plurality of dielectric coatings enters a core of the second optical fiber end section.